dag combine sext(setcc) -> vsetcc before legalize. To make this safe,

VSETCC must define all bits, which is different than it was documented
to before.  Since all targets that implement VSETCC already have this
behavior, and we don't optimize based on this, just change the 
documentation.  We now get nice code for vec_compare.ll

llvm-svn: 74978

1 files changed, 19 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 609ec82c5ad..b10751b0478 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3071,14 +3071,32 @@ SDValue DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
     }
   }
 
-  // sext(setcc x, y, cc) -> (select_cc x, y, -1, 0, cc)
   if (N0.getOpcode() == ISD::SETCC) {
+    // sext(setcc) -> sext_in_reg(vsetcc) for vectors.
+    if (VT.isVector() &&
+        // We know that the # elements of the results is the same as the
+        // # elements of the compare (and the # elements of the compare result
+        // for that matter).  Check to see that they are the same size.  If so,
+        // we know that the element size of the sext'd result matches the
+        // element size of the compare operands.
+        VT.getSizeInBits() == N0.getOperand(0).getValueType().getSizeInBits() &&
+      
+        // Only do this before legalize for now.
+        !LegalOperations) {
+      return DAG.getVSetCC(N->getDebugLoc(), VT, N0.getOperand(0),
+                           N0.getOperand(1),
+                           cast<CondCodeSDNode>(N0.getOperand(2))->get());
+    }
+    
+    // sext(setcc x, y, cc) -> (select_cc x, y, -1, 0, cc)
     SDValue SCC =
       SimplifySelectCC(N->getDebugLoc(), N0.getOperand(0), N0.getOperand(1),
                        DAG.getConstant(~0ULL, VT), DAG.getConstant(0, VT),
                        cast<CondCodeSDNode>(N0.getOperand(2))->get(), true);
     if (SCC.getNode()) return SCC;
   }
+  
+  
 
   // fold (sext x) -> (zext x) if the sign bit is known zero.
   if ((!LegalOperations || TLI.isOperationLegal(ISD::ZERO_EXTEND, VT)) &&